In a wideband code division multiple access (WCDMA) wireless communication system, a desired quality of service (QoS) may be achieved and maintained by a dual-loop feedback algorithm that utilizes outer loop power control (OLPC) and inner loop power control (ILPC). In general, a transmitter sends wireless data to a receiver, where an OLPC algorithm measures and/or estimates the QoS metric such as a block error rate (BLER) or bit error rate (BER). The OLPC algorithm determines if the measured QoS is above or below its QoS target and lowers or raises the target signal to interference ratio (SIR) accordingly. The ILPC algorithm measures a short term SIR on the dedicated physical control channel (DPCCH) pilot signal and compares it to the target generated by the OLPC.
If the short term SIR is higher than the target SIR, a command to decrease the transmitted power is sent. Otherwise, a command to increase the transmitted power is sent. The transmitter then increases or decreases its transmit power in accordance with the command, if possible. When multiple QoS targets exist for different services mapped to the same dedicated physical channel (DPCH), such as voice and video, the process may be a bit more complicated since these QoS targets may need to be met simultaneously. Since the OLPC algorithm may be limited to a single target SIR, the most demanding QoS service is chosen as the reference service, since it has the highest required SIR.
One method for handling multiple QoS targets is to switch the reference transport channel (TrCH) via a TrCH switching algorithm. That is, the OLPC measures a long-term BLER or BER on all TrCHs and selects as the reference TrCH the TrCH that is failing to meet its QoS targets by the largest amount. The target SIR updates are generated by the OLPC based off that selected reference TrCH. Using the long-term BLER or BER measurement, the OLPC determines if a different TrCH requires a higher SIR to achieve its QoS target than the current reference TrCH and switched the reference TrCH accordingly.
An issue with the above method of switching the reference TrCH, however, is that a wait period of tens or hundreds of seconds may be needed for a reliable BLER or BER estimate to determine which TrCH should be the reference TrCH. This is because a statistically reliable BLER or BER estimate requires an observation interval long enough to capture a large enough number of error events. For example, to measure a BLER of 0.001 with 100 error events, 100,000, or 100/BLER, blocks must be observed. During this observation time, data that is not on the reference TrCH may experience a substantial deterioration in quality. Accordingly, it would be beneficial to provide a method and apparatus for reference TrCH selection that is not subject to the limitations of the current state of the art.